Project Summary/Abstract Lyme disease has reached epidemic proportions in the northeastern United States and poses a substantial burden on affected communities. The illness can present with a spectrum of clinical manifestations which vary in severity and duration, including certain complications that persist after antibiotic-therapy, termed post-Lyme syndromes. However, the reasons for this range in disease severity are not clear, and biomarkers to identify patients at greater risk for adverse clinical outcomes are lacking. This presents a challenge for both physicians and patients whose symptoms do not resolve with standard antibiotic therapy. Our recent findings suggest that inappropriate immune responses, which are shaped at least in part by host genetics, are an important factor in these outcomes. We previously identified a single-nucleotide polymorphism in the host TLR1 gene (TLR1- 1805GG SNP) which leads to excessive inflammation and more severe disease, including more symptomatic early infection and a greater risk for antibiotic-refractory Lyme arthritis, a post-Lyme complication of this disease. These findings provided a new paradigm for studying inappropriate immune responses and untoward clinical outcomes in Lyme disease. However, as implied in our preliminary findings with LCE3 SNPs, in human disease multiple genetic loci likely contribute to immune dysregulation and greater disease severity. In this proposal, we are applying our multi-prong approach using cutting-edge methodologies, clinical samples from well-defined patients, and functional studies in cells and tissue to identify a greater range of host genetic polymorphisms that may play a role in adverse clinical outcomes in Lyme disease and to elucidate the mechanisms by which these factors lead to excessive inflammation. We propose 2 specific aims: Aim 1: To identify host genetic risk factors associated with more severe disease in EM patients with mild vs severe disease and in LA patients with antibiotic-responsive vs antibiotic-refractory course, using targeted GWAS- based ImmunoArray; Aim 2: To evaluate the functional consequence of implicated LCE3 SNPs in patients by assessing their effect on immune phenotypes and transcriptome profiles in tissue, and in cell culture by interrogating key inflammatory and regulatory pathways affected by candidate SNP/gene using RNA sequencing and RNA-interference. The work proposed here will provide new insights into pathogenesis and is likely to lay the groundwork for novel diagnostic approaches for patients at greater risk for severe disease, including post-Lyme syndromes. The ability to identify such patients could help guide more effective treatment strategies such as combination of antibiotics and immunotherapy. Finally, these findings and model systems may be valuable in understanding other post-infectious and chronic inflammatory conditions.